I'm afraid all I remember is:
- Magic was based on true names
- The hero was pulled from the real world into another one
- At the climax of the book the hero said his full name linking him in some manner with the goddess of that world.
- I think his middle or last name had a prefix like "Mac"
- I think the book was written in the 80's, I read it in the early 90's.
- AFAIK It was not part of a series.
Does anyone know what this is?